-- countBCD
-- 4-bit presettable up/down BCD counter with asynchronous clear and load
-- and Carry IN (CIN) and Carry Out (COUT).
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;

ENTITY countBCD IS
	PORT(       
        clk, CIN				: IN    STD_LOGIC;
        clear, load, UpDown		: IN    STD_LOGIC;
		p						: IN	INTEGER RANGE 0 TO 15;
		COUT					: OUT	STD_LOGIC;
        q						: OUT   INTEGER RANGE 0 TO 15);
END countBCD;

ARCHITECTURE a OF countBCD IS
	BEGIN
	PROCESS (clk, clear, load)
	VARIABLE    cnt       : INTEGER RANGE 0 TO 15;
		BEGIN
			IF (clear = '0' ) THEN	-- Asynchrnous clear
				cnt	:=	0;
			ELSIF (load = '1' and clear = '1') THEN	-- Asynchronous presettable load
				cnt := p;
			
			ELSE
				IF (clk'EVENT AND clk = '1') THEN
					IF (CIN = '1' and UpDown = '1') THEN
						cnt := cnt - 1;
						if (cnt =15) then cnt := 9; END IF; 
					ELSIF (CIN = '1' and UpDown = '0') THEN
						cnt := cnt + 1;
						if (cnt =10) then cnt := 0; END IF;
					END IF;
				END IF;
			END IF;
			q	<=	cnt;

			-- COUT=1 at 9 for up count and COUT=1 at 0 for down count.
			IF (cnt = 0 and UpDown = '1') THEN
				COUT <=	'1';
			ELSIF (cnt = 9 and UpDown = '0') THEN
				COUT <=	'1';
			ELSE
				COUT <=	'0';
			END IF;
		END PROCESS;
	END a;